brendonm, no problem When I started thinking about this project I thought that a piece of ground silver steel (drill rod) in a reamed hole would be sufficient. As I move on it became clear that this was nowhere near good enough so I am no trying to reduce the clearances as much as I can with the equipment that I have.

The plunger is hardened and the pump body is mild steel. I have no idea how long they will last, but if I can get it to run even for a few minutes I will be happy

Roger, Have only just become aware of both this thread and your other one on making a horizontal 2 stroke diesel engine. I have now read threads both from start to finish and am full of admiration for what you are doing and the skill you are doing it with. I will be following both with upmost interest and wish you well - I sincerely hope you are successful in your quest and am sure you will be, seeing what has gone before.

Whenever I have wondered in idle moments about the making of a model diesel the big block has always been "but to be a diesel it needs a HP fuel pump and injector, not things that the vast majority of home workshops can produce". Having worked with diesels of all sizes extensively in an earlier life I am only too well aware to which the very fine tolerances diesel pumps and injectors are made, which is why I thought it beyond the scope of most workshops. You seem to be showing a way of achieving that standard of engineering required.

Also of interest is the use of the injectors for low pressure use in petrol or glow plug engines, in particular in 2 stroke engines where instead of the fuel/oil/air mixture being pumped into the cylinder via the crankcase and the action of the piston, the air, devoid of fuel or fuel/oil glow plug mixture, is pumped into the cylinder via a blower and the fuel injected after the exhaust port has closed. This would have the benefit of ensuring complete scavenging without blowing excess unburnt fuel into the exhaust. Whether the oil in the fuel/oil mix would cause a problem in blocking the injector nozzle holes I don't know; in theory not, as it readily vaporises going through a carby, but the injector nozzle holes present a much finer hole. Just a thought.

Thank you for your interest Chris I know others have made small, true, diesels successfully and I hope that I can follow in their footsteps I think that I am moving in the right direction, but lapping to these tolerances is definitely something to practice

A sort of success It was a sunny evening here so I thought I would try the petrol (gasoline) injection on my horizontal engine.

I warmed it up with the carburettor and then fitted the injection manifold with a carb as a throttle. The tank was filled with petrol, there may have still been some alcohol in the pipes from the last trial. Then came the fun, I had a throttle lever, a stroke adjustment handwheel for the pump and a starter button to press (and a drip oiler for the cylinder to remember) all with two hands. After various adjustments it started Control was somewhat difficult as due to the leakage from the system the fuel quantity increased significantly with speed so as I opened the throttle I had to reduce the pump stroke. If the revs dropped for any reason it would just stop and I had to increase the stroke to maximum again to get it to start. There was a significant quantity of fuel dripping out of the injector pressure adjustment screw.

So it worked, my calculations regarding the size of pump required were not too far out, I just have to tighten up the tolerances even more (actually it might be better with diesel as it is more viscous and may leak less).

Apologies for the video quality, it was starting to get dark and I was quite excited

I dismantled the injector to see what I could do to tighten up the tolerances and found that I had left the strong spring in This gives a needle loading of around 10N which is a calculated opening pressure of 50bar, rather more than is needed for manifold injection. If we get some good weather I will try again with the correct spring.

I have also been looking at the pump again. I originally thought that using a metering helix like the full size pumps would be too difficult, but I came across a design that just used a simple helical groove. A quick sketch suggests that a groove around 0.6mm wide and a pitch of 4mm could work. My lathe only goes to a 3mm pitch but by playing with the gears I can reach 4mm, which should be ok as it will only be hand turned. If I can mount the Proxxon tool with a cutting disc at the required angle and on centre I will have a go at cutting a helix on a scrap plunger.

I put the correct spring in the injector and had another more successful trial There was more throttle response than I expected and it generally ran quite steadily. One puzzling point was the appearance of bubbles in the fuel pipe to the injection pump As far as I can see the only possible air leak could be down the plunger and if air leaked in there should have been a significant fuel leak out

By the way, I had a look at your helix plunger diagram, and I look forward to seeing it be made. Mind you, I will have to wait until you build it to understand what I was looking at (d'oh)

Keep up the good work. I've been trying to build a simple part that requires a smidgen of accuracy (I'm on my fourth attempt ), and I now have an appreciation for how much precision is required in a fuel injection pump!